J/ApJ/945/119 The Oceanus moving group members from Gaia DR3 (Gagne+, 2023) ================================================================================ The Oceanus moving group: a new 500 Myr old host for the nearest brown dwarf. Gagne J., Moranta L., Faherty J.K., Kiman R., Couture D., Larochelle A.R., Popinchalk M., Morrone D. =2023ApJ...945..119G ================================================================================ ADC_Keywords: Associations, stellar; Photometry, infrared; Optical; YSOs; Radial velocities; Proper motions Keywords: Stellar associations ; Open star clusters ; Stellar kinematics ; Brown dwarfs Abstract: We report the discovery of the Oceanus moving group, a ~500Myr old group with 50 members and candidate members at distances 2-50pc from the Sun, using an unsupervised clustering analysis of nearby stars with Gaia DR3 data. This new moving group includes the nearest brown dwarf WISE J104915.57-531906.1 AB (Luhman 16 AB) at a distance of 2pc, which was previously suspected to be young (600-800Myr) based on a comparison of its dynamical mass measurements with brown dwarf evolutionary models. We use empirical color-magnitude sequences, stellar activity, and gyrochronology to determine that this new group is roughly coeval with the Coma Ber open cluster, with an isochronal age of 510+/-95Myr. This newly discovered group will be useful to refine the age and chemical composition of Luhman 16 AB, which is already one of the best substellar benchmarks known to date. Furthermore, the Oceanus moving group is one of the nearest young moving groups identified to date, making it a valuable laboratory for the study of exoplanets and substellar members, with eight brown dwarf candidate members already identified here. Description: We used the HDBSCAN algorithm (McInnes & Healy 2017arXiv170507321M) to search for new clusters of stars within 200pc of the Sun based on Gaia DR3 data with a method similar to that of Moranta+ (2022, J/ApJ/939/94). See Section 2. Objects: ------------------------------------------------------------------------- RA (ICRS) DE Designation(s) ------------------------------------------------------------------------- Oceanus Moving Group = NAME Oceanus Moving Group ------------------------------------------------------------------------- File Summary: -------------------------------------------------------------------------------- FileName Lrecl Records Explanations -------------------------------------------------------------------------------- ReadMe 80 . This file table1.dat 157 89 List of members and candidate members of the Oceanus moving group table2.dat 140 89 Kinematics of the Oceanus moving group table3.dat 109 227 Radial velocities of the Oceanus moving group table4.dat 154 89 Galactic coordinates and space velocities of the Oceanus moving group -------------------------------------------------------------------------------- See also: III/123 : Dwarf K and M stars of small proper motion (Stephenson 1986) IX/10 : ROSAT All-Sky Bright Source Catalogue (1RXS) (Voges+ 1999) VII/233 : 2MASS All-Sky Extended Source Catalog (XSC) (IPAC/UMass, 2003-2006) I/297 : NOMAD Catalog (Zacharias+ 2005) III/254 : 2nd Cat. of RVel with Astrometric Data (Kharchenko+, 2007) I/311 : Hipparcos, the New Reduction (van Leeuwen, 2007) II/319 : UKIDSS-DR9 LAS, GCS and DXS Surveys (Lawrence+ 2012) I/329 : URAT1 Catalog (Zacharias+ 2015) I/345 : Gaia DR2 (Gaia Collaboration, 2018) III/284 : APOGEE-2 data from DR16 (Johnsson+, 2020) II/365 : CatWISE2020 catalog (updated version 28-Jan-2021) (Marocco+, 2021) I/355 : Gaia DR3 Part 1. 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(Shkolnik+, 2009) J/ApJ/723/684 : NIRSPEC ultracool dwarf RVel survey (Blake+, 2010) J/ApJ/725/875 : Chromospheric activity for CPS stars (Isaacson+, 2010) J/ApJS/190/77 : Detailed analysis of cool WDs in the SDSS (Kilic+, 2010) J/ApJS/190/100 : NIR proper motion survey using 2MASS (Kirkpatrick+, 2010) J/MNRAS/403/1949 : UBV(RcIc)JHK photometry of HIP nearby stars (Koen+, 2010) J/A+A/514/A97 : High-res. spectra of Late-type stars (Lopez-Santiago+ 2010) J/A+A/521/A12 : Rvel of nearby late-type stars (Maldonado+, 2010) J/ApJS/197/19 : First brown dwarfs discovered by WISE (Kirkpatrick+, 2011) J/ApJ/733/L9 : Stellar rotation for 71 NGC 6811 members (Meibom+, 2011) J/AJ/141/97 : SDSS DR7 M dwarfs (West+, 2011) J/ApJS/201/19 : Hawaii Infrared Parallax Program. I. (Dupuy+, 2012) J/ApJ/753/156 : T/Y brown dwarfs with WISE photometry (Kirkpatrick+, 2012) J/AJ/143/103 : New white dwarfs (Sayres+, 2012) J/AJ/143/80 : Low-mass stars of beta Pic & AB Dor (Schlieder+, 2012) J/ApJ/758/56 : Young M dwarfs within 25pc. II. Kinematics (Shkolnik+, 2012) J/MNRAS/433/457 : 76 T dwarfs from the UKIDSS LAS (Burningham+, 2013) J/ApJS/205/6 : T dwarf population revealed by WISE (Mace+, 2013) J/ApJ/783/122 : AllWISE motion survey (Kirkpatrick+, 2014) J/AJ/147/20 : Spectroscopy of 447 nearby M dwarfs (Newton+, 2014) J/AJ/147/34 : SpeX library of L-type dwarfs (Schneider+, 2014) J/A+A/566/A132 : Teff and L for stars in 7 open clusters (Silaj+, 2014) J/A+A/583/A85 : Binaries in beta Pic moving group (Alonso-Floriano+, 2015) J/ApJ/798/73 : BANYAN All-Sky Survey (BASS) cat. V. YMGs (Gagne+, 2015) J/A+A/581/A73 : Luhman 16AB X-shooter spectra (Lodieu+, 2015) J/ApJS/225/10 : Kinematic analysis of M7-L8 dwarfs (Faherty+, 2016) J/ApJ/833/96 : Hawaii IR plx program. II. Ultracool dwarfs (Liu+, 2016) J/A+A/596/A116 : Radial velocities of K-M dwarfs (Sperauskas+, 2016) J/MNRAS/469/2102 : White dwarf population from the SDSS DR12 (Anguiano+, 2017) J/ApJ/838/73 : BD* surface gravities with Keck/NIRSPEC (Martin , 2017) J/AJ/153/257 : Comoving stars in Gaia DR1 (Oh+, 2017) J/A+A/615/A165 : EWs of 13 red giants in IC 4756 (Bagdonas+, 2018) J/ApJS/234/1 : Cat. of M, L, & T dwarfs from PS1 3{pi} Survey (Best+, 2018) J/A+A/616/A108 : Cool stars chromospheric activity cat. (Boro Saikia+, 2018) J/AJ/155/34 : The NIR spectra of neighboring L dwarfs (Cruz+, 2018) J/ApJ/862/138 : BANYAN. XIII. Nearby young assoc. with Gaia (Gagne+, 2018) J/ApJ/856/23 : BANYAN. XI. The BANYAN {Sigma} algorithm (Gagne+, 2018) J/AJ/155/39 : Variability data of TIC sources with KELT (Oelkers+, 2018) J/A+A/619/L8 : Ultra-cool dwarfs candidates in Gaia DR2 (Reyle, 2018) J/A+A/616/A7 : Gaia DR2 RVel standard stars cat. (Soubiran+, 2018) J/A+A/621/A126 : CARMENES input catalog of M dwarfs. IV. (Diez Alonso+ 2019) J/A+A/623/A72 : Binarity of HIP stars from Gaia pm anomaly (Kervella+, 2019) J/AJ/158/122 : Local structure & SFH of the MW (Kounkel+, 2019) J/ApJS/243/28 : M-type star magnetic activities (Lu+, 2019) J/A+A/627/A4 : Praesepe (NGC 2632) and its tidal tails (Roeser+, 2019) J/A+A/621/L2 : Hyades tidal tails revealed by Gaia DR2 (Roeser+, 2019) J/ApJ/877/12 : Coma Ber & Neighbor Stellar Group tidal tails (Tang+, 2019) J/ApJ/901/93 : Model atm. analysis of hot WDs from SDSSDR12 (Bedard+, 2020) J/AJ/159/257 : Hawaii IR plx prog. IV. L0-T8 BDs with UKIRT (Best+, 2020) J/A+A/640/A1 : Portrait Galactic disc (Cantat-Gaudin+, 2020) J/A+A/636/A36 : Absolute RVel of CARMENES M dwarfs (Lafarga+, 2020) J/A+A/636/A74 : HARPS radial velocity database (Trifonov+, 2020) J/AJ/160/38 : Spitzer var. detections of 79 brown dwarfs (Vos+, 2020) J/AJ/161/42 : Volume-limited sample of cool dwarfs. I. L0-T8 (Best+, 2021) J/MNRAS/508/3877 : Catalogue of white dwarfs in Gaia EDR3 (Gentile+, 2021) J/ApJ/917/23 : SPYGLASS. I. Mapping young stellar structures (Kerr+, 2021) J/ApJS/253/7 : A full-sky census of BDs within 20pc (Kirkpatrick+, 2021) J/A+A/652/A28 : Activity across the M dwarf domain (Lafarga+, 2021) J/ApJS/254/20 : Stellar groups in Taurus from Gaia DR2 & LAMOST (Liu+, 2021) J/A+A/664/A70 : Lithium depletion boundary in assoc. (Galindo-Guil+, 2022) J/A+A/657/L3 : Rot. periods of Group X candidate members (Messina+, 2022) J/ApJ/939/94 : New assoc. in Gaia DR3 solar neighborhood (Moranta+, 2022) Byte-by-byte Description of file: table1.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 28 A28 --- Name Identifier 32 A1 --- f_Name [d] d=likely an unresolved binary star 34- 52 I19 --- Gaia ? Gaia DR3 identifier 54- 55 A2 --- Type Member type code (G2) 57- 60 A4 --- Origin Origin of the sample (1) 62- 70 A9 --- SpType Spectral type (2) 72- 73 I2 h RAh Hour of Right Ascension (J2000) (G1) 75- 76 I2 min RAm Minute of Right Ascension (J2000) 78- 79 I2 s RAs Second of Right Ascension (J2000) 81 A1 --- DE- Sign of the Declination (J2000) (G1) 82- 83 I2 deg DEd Degree of Declination (J2000) (G1) 85- 86 I2 arcmin DEm Arcminute of Declination (J2000) 88- 91 F4.1 arcsec DEs Arcsecond of Declination (J2000) 93- 98 F6.3 mag Gmag [5.6/21]? Gaia DR3 G band magnitude 100-105 F6.3 mag W1mag [3.9/16.5]? WISE 3.4 micron band magnitude 107-117 A11 --- Youth Sign(s) of youth (3) 119-123 F5.2 km/s DelUW [0.3/19.4]? Total space velocity difference (4) 125-127 A3 --- Obs Observables (5) 129-133 A5 --- Assoc Best matching BANYAN {Sigma} association (6) 135 A1 --- l_PMm Upper limit flag on PMm 136-139 F4.1 --- PMm [22/99.9]? Best matching BANYAN {Sigma} association membership probability 143-154 A12 --- Rej Reason(s) for rejection (7) 156-157 I2 --- Ref [1/28] Reference code (see refs.dat file) -------------------------------------------------------------------------------- Note (1): Survey sample from which the star was identified as a Oceanus moving group candidate member. Code as follows: HDBS = Initial sample from HDBSCAN; Gaia = Additional search from Gaia DR3 (I/355); UCS = UltracoolSheet (Best+ 2020, doi: 10.5281/zenodo.4169085); BASS = BASS survey input sample (Gagne+ 2015, J/ApJ/798/73) CW = CatWISE2020 (II/365); Comp = Companion to a member or candidate member of the Oceanus moving group. Note (2): Spectral types inside parentheses indicate an estimation based on Gaia or WISE photometry. See the Ref column and Note (7) to obtain which photometric bands the spectral types of specific stars were estimated from. Note (3): Available evidence suggesting a potentially young age. Code as follows: gy = gyrochronology; dm = dynamical mass; uv = UV emission; H{alpha} = strong H{alpha} emission; ac = spectroscopic indices associated with a strong stellar activity; xr = x-ray emission; rd = red near-infrared colors indicative of a low surface gravity; si = spectral indices indicative of a low surface gravity; Note (4): in Galactic space velocity between the star and the average Galactic space velocity of the Oceanus moving group members. Note (5): Observables included as an input to determine the BANYAN {Sigma} probabilities. m: proper motion; n: radial velocity; v: parallax. Note (6): Best matching BANYAN {Sigma} model associated membership probability. The hypotheses are abbreviated as follows: OCEMG = Oceanus moving group; COL = Columba association (Torres+ 2008hsf2.book..757T); ARG = Argus association (Torres et al. 2008); CARN = Carina-Near moving group (Zuckerman+ 2006ApJ...649L.115Z) COH59 = corona of the Oh+ (2017, J/AJ/153/257) Group 59 (Moranta+ 2022, J/ApJ/939/94); ABDMG = AB Doradus moving group (Zuckerman+ 2004ApJ...613L..65Z). Note (7): Available evidence rejecting a plausible membership in the Oceanus moving group. Code as follows: kin = kinematics; gy = gyrochronology; ac = spectroscopic indices associated with a weak stellar activity; bl = blue near-infrared colors inconsistent with a young age; cm = Gaia DR3 color-magnitude diagram position inconsistent with the age of the Oceanus moving group; ca = white dwarf cooling age inconsistent with the age of the Oceanus moving group; li = lithium equivalent width indicates an older age; sp = likely to be a spurious Gaia parallax solution. -------------------------------------------------------------------------------- Byte-by-byte Description of file: table2.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 28 A28 --- Name Identifier 30- 48 I19 --- Gaia ? Gaia DR3 identifier 50- 51 A2 --- Type Member type code (G2) 53- 54 I2 h RAh Hour of Right Ascension (J2000) (G1) 56- 57 I2 min RAm Minute of Right Ascension (J2000) 59- 60 I2 s RAs Second of Right Ascension (J2000) 62- 62 A1 --- DE- Sign of the Declination (J2000) (G1) 63- 64 I2 deg DEd Degree of Declination (J2000) (G1) 66- 67 I2 arcmin DEm Arcminute of Declination (J2000) 69- 70 I2 arcsec DEs Arcsecond of Declination (J2000) 72- 79 F8.2 mas/yr pmRA [-2755/254]? Proper motion along RA times cosDE 81- 85 F5.2 mas/yr e_pmRA [0.01/20]? Uncertainty in pmRA 87- 93 F7.2 mas/yr pmDE [-446/359]? Proper motion along DE 95- 99 F5.2 mas/yr e_pmDE [0.01/20]? Uncertainty in pmDE 101-106 F6.2 km/s RVel [-40.1/26]? Radial velocity 108-111 F4.2 km/s e_RVel [0.04/6]? Uncertainty in RVel 113-115 I3 --- o_RVel [1/113]? Number of observations in RVel (8) 117-122 F6.2 mas plx [14.26/501]? Parallax 124-127 F4.2 mas e_plx [0.01/3]? Uncertainty in plx 129-131 F3.1 --- RUWE [0.8/6.5]? Gaia DR3 RUWE value 133-134 I2 --- r_Pos [31/36]? Coordinate reference (see refs.dat file) 136-137 I2 --- r_pm [31/40]? Reference code for proper motions (see refs.dat file) 139-140 I2 --- r_plx [31/40]? Reference code for plx (see refs.dat file) -------------------------------------------------------------------------------- Note (8): Number of individual radial velocity measurements that were combined into the measurement reported here. See Table 5 for individual measurements and their references. -------------------------------------------------------------------------------- Byte-by-byte Description of file: table3.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 28 A28 --- Name Identifier 30- 48 I19 --- Gaia Gaia DR3 identifier 50- 51 A2 --- Type Member type code (G2) 53- 54 I2 h RAh Hour of Right Ascension (J2000) (G1) 56- 57 I2 min RAm Minute of Right Ascension (J2000) 59- 64 F6.3 s RAs Second of Right Ascension (J2000) 66 A1 --- DE- Sign of the Declination (J2000) (G1) 67- 68 I2 deg DEd Degree of Declination (J2000) (G1) 70- 71 I2 arcmin DEm Arcminute of Declination (J2000) 73- 77 F5.2 arcsec DEs Arcsecond of Declination (J2000) 79- 86 F8.4 km/s RVel [-40.1/30] Radial velocity 88- 93 F6.4 km/s e_RVel [0.0003/6] Uncertainty in RVel 95- 96 I2 --- o_RVel [1/55] Number of observations in RVel 98- 106 F9.4 yr Epoch [1996/2018.2]? Fractional year of the observation on which the radial velocity measurement is based 108- 109 I2 --- Ref [41/58] Reference code (see refs.dat file) -------------------------------------------------------------------------------- Byte-by-byte Description of file: table4.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 28 A28 --- Name Identifier 30- 48 I19 --- Gaia ? Gaia DR3 identifier 50- 51 A2 --- Type Member type code (G2) 53- 54 I2 h RAh Hour of Right Ascension (J2000) (G1) 56- 57 I2 min RAm Minute of Right Ascension (J2000) 59- 60 I2 s RAs Second of Right Ascension (J2000) 62 A1 --- DE- Sign of the Declination (J2000) (G1) 63- 64 I2 deg DEd Degree of Declination (J2000) (G1) 66- 67 I2 arcmin DEm Arcminute of Declination (J2000) 69- 70 I2 arcsec DEs Arcsecond of Declination (J2000) 72- 79 F8.4 pc X [-42.6/69.2]? Galactic X coordinate, centered on Sun & positive towards the Galactic center 81- 86 F6.4 pc e_X [0.0001/5]? Uncertainty in X 88- 95 F8.4 pc Y [-22.6/53.4]? Galactic Y coordinate centered on Sun & positive towards the direction of Galactic rotation, parallel to the Galactic plane 97- 102 F6.4 pc e_Y [0.0003/5]? Uncertainty in Y 104- 111 F8.4 pc Z [-17.4/52]? Galactic Z coordinate centered on Sun & positive outside the Galactic plane in the North Galactic hemisphere, normal to the Galactic plane such that XYZ form a right-handed coordinate system. 113- 118 F6.4 pc e_Z [0.0001/2]? Uncertainty in Z 120- 125 F6.2 km/s U [-34.2/-7.7]? Velocity towards Galactic center (rate of change in X), relative to the Solar motion 127- 130 F4.2 km/s e_U [0.01/5]? Uncertainty in U 132- 137 F6.2 km/s V [-32.1/-16]? Velocity along Galactic rotation (rate of change in Y), relative to the Solar motion 139- 142 F4.2 km/s e_V [0.01/4]? Uncertainty in V 144- 149 F6.2 km/s W [-15/0.2]? Velocity normal to the Galactic plane toward North Galactic hemisphere (rate of change in Z), relative to the Solar motion 151- 154 F4.2 km/s e_W [0.01/3]? Uncertainty in W -------------------------------------------------------------------------------- Global notes: Note (G1): All coordinates from Gaia DR3 are J2000, ep=2016.0 while the rest are specific to the individual literature source that is cited. The coordinates are not meant for precise astrometry but rather to help identify each star and binary component. Note (G2): Membership type, indicating a subjective assessment of how robust the membership is considered to be. Code as follows: BF = Bona fide member (17 occurrences) HM = High-likelihood candidate member (9 occurrences) CM = Candidate member (25 occurrences) LM = Low-likelihood candidate member (5 occurrences) R = Rejected candidate member (33 occurrences) -------------------------------------------------------------------------------- History: From electronic version of the journal ================================================================================ (End) Prepared by [AAS], Emmanuelle Perret [CDS] 07-Feb-2025